1. Field of the Invention
The present invention relates generally to a method of acquiring a Global Positioning System (GPS) signal in a communication system and a system and terminal using the method, and in particular, to a method of receiving assistance information for acquiring an initial GPS signal in a communication system and a system and terminal using the method.
2. Description of the Related Art
In general, it takes a long time for a terminal in a mobile communication system to acquire a Global Positioning System (GPS) signal required to determine its position. In order to reduce an initial GPS signal acquisition time, Assisted GPS (AGPS) technology for providing rough code phase and Doppler frequency information is used, wherein the code phase and Doppler frequency information is called Acquisition Assistance (AA) data. Since a code and frequency search range can be reduced using the AA data when a receiver processes a GPS signal, the initial GPS signal acquisition time can be reduced.
A method of receiving AA data in a conventional mobile communication system will now be described with reference to FIG. 1.
FIG. 1 is a block diagram illustrating a conventional mobile communication system uses a GPS function. Referring to FIG. 1, a mobile communication system 100 includes GPS satellites 101, an Assisted GPS (AGPS) server 103, a communication provider server 105, a base station 107, and a terminal 109. A method for the terminal 109 to receive AA data will now be described. The terminal 109 requests the AGPS server 103 for the AA data. When the AGPS server 103 receives the AA data request from the terminal 109 via the base station 107 and the communication provider server 105, the AGPS server 103 detects the base station 107 with which the terminal 109 currently communicates and determines a rough position of the terminal 109 based on the detected base station 107.
The AGPS server 103 calculates a code phase and a Doppler frequency of a GPS signal using the rough position of the terminal 109 and positions of the GPS satellites 101 and transmits AA data 113 including the calculated code phase and Doppler frequency to the terminal 109. The terminal 109 receives the AA data and uses the received AA data for a GPS signal search.
According to the conventional technology for generating and transmitting AA data using a mobile communication network, the AA data can be generated only if a mobile terminal provides information on a base station with which the mobile terminal communicates to an AGPS server. In addition, a process for the mobile terminal to request the AGPS server for AA data and connect a traffic channel to receive data provided by the AGPS server is required. Thus, since a method for a mobile terminal to request for AA data does not exist in a one directional broadcasting system such as a Digital Multimedia Broadcasting (DMB) system, the conventional method cannot be applied to the one-directional broadcasting system.